In fact, you can write a new application or another viewer plugin, but it is almost impossible to use them. You cannot change the bookshelf in order to recognize a new file format and start your new plugin when you open that file.

It is very strange to have a SDK and then not allow the software to be deployed. I was surprised that BeBook do not seem to mind folk running alternative firmware on their device. Amazon is presumably releasing all the source code it needs to, but they are never going to make it easy to run 3rd party firmware on the Kindle.